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Saturday, 15 October 2016

How to Prevent Cracks in Concrete? Causes & Repairs of Cracks in Concrete (Part 2)

(2) Proper Concrete Mix Design and use of Quality Materials

The concrete itself must be properly proportioned, and properly mixed.  If you use too little cement, you can almost guarantee cracks.  Using too much water
will make the concrete weak, leading to cracking.
Use good quality aggregates so will produce lower shrinkage concrete.  Hard, dense aggregate, using a large top size aggregate and optimizing the gradation of the aggregate is able to reduce the shrinkage of the concrete.
If the aggregate is of poor quality, maximizing the size, gradation, and content may have little effect on the concrete shrinkage. Mixing large aggregate with poor qualities to a mid-size aggregate with good properties may increase the shrinkage of the concrete.
Avoid the use of shrinkage-promoting admixtures (such as accelerators, dirty aggregate which increases water demand and using a cement with high shrinkage characteristics.

(3) Finishing of Concrete Surface

Use proper finishing techniques and proper timing during and between finishing operations. Flat floating and flat troweling are often recommended.
Avoid overworking the concrete, especially with vibrating screeds. Overworking causes aggregate to settle and bleed water and excess fines to rise.
Don’t finish the concrete when there is bleed water on the surface, finishing leads the water back to concrete instead of evaporating thus leading to cracks.

(4) Proper Curing of Concrete

Stop rapid loss of water from surface or drying of concrete due to hydration (liquid concrete converts to plastic and then to solid state) causes drying of the slab, so it’s recommended to cure the slab for several days.
As soon as the concrete on slab sets its general practice to make boundary with mortar on the slab and keep it filled with water. Cover slab with cotton mats soaked with water or spray on a curing compound also prevents loss of water.
The concrete should not be subjected to load during the curing period, which can last up to one month.
Proper Curing of Concrete
Curing of Concrete to Prevent Cracks

(5) Proper Placement and Vibration of Concrete

Properly placed, vibrated, finished concrete reduces the chances of producing cracks. Properly vibrate to release entrapped air which later leads to cracks.
Vibration of Concrete

(6) Proper Compaction of Soil to Prevent Settlement Cracks in Concrete

The area below the concrete slab has to be compacted properly and in layers so as to ensure against settlement of soil later. If the soil is left loose it will settle over time and create cracks on surface. This applies in the home as well as constructions on highways.
Compaction of Soil to Prevent Settlement Cracks in Concrete

(7) Providing Control Joints in Concrete

Control joints should be located at regular intervals so as to adjust the shrinkage of concrete. Generally, for 4-inch depth of slab, joints are provided 8 to 12 ft. apart. Control joints are pre-planted cracks. An engineer should have an idea that concrete will crack at control joints instead of cracking any other location.
Providing Control Joints in Concrete

Some Other Preventive Control Measures for Cracks in Concrete:

  • Applying good acrylic silicone sealer yearly to concrete works
  • Avoid calcium chloride admixtures
  • Prevent extreme changes in temperature.
  • Consider using a shrinkage-reducing admixture
  • Warm the subgrade before placing concrete on it during cold weather
  • Consider using synthetic fibers to help control plastic shrinkage cracks.
Hope this helps? Please make your contributions.....

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